Acid chloride

From Academic Kids

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General Chemical Structure of an Acyl Chloride

In organic chemistry, an acid chloride (or acyl chloride) is an organic chemical compound which is a very reactive derivative of a carboxylic acid. In its molecule, an acyl chloride has the reactive functional group -CO-Cl. An acyl chloride has the general formula RCOCl where R is an organic radical group. See the general chemical structure of an acyl chloride at right.

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Example of acyl chloride:
Acetyl Chloride

Acyl chlorides are a subset of acyl halides and undergo many of the chemical reactions mentioned under Acyl halide. A specific example of an acyl chloride is acetyl chloride (IUPAC name: ethanoyl chloride) CH3COCl. See the simple diagram at left.

Chemical reactions

Acid chlorides are very reactive, the presence of the chlorine on the carbonyl carbon makes it a very good electrophile, since both the oxygen and chlorine are strongly electron withdrawing, giving the carbon a large partial positive charge. This means even a weak nucleophile can attack the carbon. Since a chloride ion is a good leaving group, this is a very useful compound synthetically, it can be used to prepare any carboxylic acid derivative: an acid anhydride, an ester or an amide by reacting acid chlorides with: a salt of a carboxylic acid, an alcohol, or an amine respectively. Acid chlorides will also react with water or a Gilman reagent (lithium diorganocopper compound). In most of these reactions, HCl (hydrogen chloride or hydrochloric acid) is also formed.


Because acyl chlorides are such reactive compounds, they have toxicity and special precautions should be taken handling them. They are lachrymatory chemicals because they can react with water at the surface of the eye producing hydrochloric and organic acids irritating to the eye. Similar problems can result if one inhales acyl chloride vapors.


Acyl chlorides are often prepared by reacting a carboxylic acid with thionyl chloride.

R-COOH + SOCl2 → R-COCl + SO2 + HCl

The sulfur dioxide (SO2) and hydrogen chloride (HCl) generated are both gases which can leave the reaction vessel, driving the reaction forward. They are also both toxic gases. Acyl chlorides can also be prepared using certain phosphorus chloride reagents such as phosphorus trichloride or phosphorus pentachloride.da:Syrechlorid


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